PARIS, Feb 16 (Reuters) - As he quietly bides his time preparing a possible 2017 political comeback, former French President Nicolas Sarkozy has a winning asset very much in the spotlight - his wife.

Beaming from billboards, magazines and the stage, singer-songwriter and ex-supermodel Carla Bruni has embraced her post-first lady life in a very public way, resuming her career while generating media buzz over the future plans of her husband.

The role of France's "first ladies" - and what they do once they no longer have that title - has been a matter of comment after photos allegedly showing President Francois Hollande's night-time visits to a mistress triggered the break-up of his relationship with long-time partner Valerie Trierweiler.

Meanwhile, the previous first lady, who married Sarkozy during his first year in office in 2008, still makes waves. Political watchers and brand analysts say 46-year-old brunette Bruni is still the perfect foil to Sarkozy, who jokes he is "the retired guy" since his May 2012 electoral defeat by Hollande.

"First, she's gorgeous, second, she's classy, and third, she seems nice," said Thomas Guenole, political scientist and author of "Nicolas Sarkozy, Chronicle of an Impossible Comeback?"

Since Sarkozy's defeat, Bruni has released her fourth album and launched a tour to promote it, while dipping her toe back into the high-glamour modelling world as the face of Italian jeweller Bulgari and with ads for Parrot Zik headphones.

She's been photographed in the front row at a Paris fashion show and even showed up at a campaign stop for Sarkozy's former spokeswoman, now running for his conservative camp as Paris mayor in March city hall elections.

"Because Nicolas Sarkozy is planning a comeback, everyone is looking at it with a political eye, and not just a celebrity-focused one," said Bertrand Chovet, managing director of the Interbrand agency in Paris.

He said occasional Sarkozy appearances at Bruni's concerts also "humanise" the ex-president, who shakes hands and signs autographs from conservative voters waving "Come Back" posters.

Despite a post-defeat promise to leave politics for good, Sarkozy has since hinted he may return "out of duty".

He is the overwhelming favourite among right-wing voters to run for president in 2017 as the candidate of his fractious UMP party. In a poll last month he was picked as best candidate by 62 percent of right-leaning voters, compared to 14 percent for his closest challenger, ex-foreign minister Alain Juppe.

Bruni's agent did not respond to an interview request. Sarkozy's office did not respond to a message seeking comment.

"MODERN PRINCESS"

Bruni's active career piqued the interest of a public used to first ladies who either devoted themselves to philanthropy or combined charitable work with low-profile political roles, as did Jacques Chirac's wife Bernadette, a town councillor.

Bruni also managed to avoid the public animosity suffered by Trierweiler, a journalist whose outspokenness jarred with the French, according to opinion polls.

Turin-born Bruni, who immigrated to France as a child, says politics do not interest her. She cultivated a domestic image in the 2012 presidential campaign, wearing slouchy sweaters with little makeup and talking about her favourite TV shows.

Casting herself as the limelight-shunning spouse content to spend her evenings on the couch helped counteract Sarkozy's image as a lover of Rolexes and yachts.

For advertisers like Bulgari, Bruni provides a unique combination of political and artistic glamour.

"She's Italian, she's cosmopolitan, she was the president's wife, she's hung out with the big guns not only in the artistic and music world but in the political milieu," said Chovet. "All considered, she's a princess of modern times."

Bulgari - which is owned by LVMH, whose chief executive was a witness at the Sarkozy-Bruni wedding - did not respond to interview requests.

A spokeswoman for the headphone maker Parrot said it picked Bruni as its face not for her political associations but because she was "very free in her choices" and a bit "non-conformist."

Parrot said Bruni was not paid for the ad. Instead, the company donated to a music charity her foundation supports.

The tough-talking Sarkozy had a polarising image and is reviled by many French on the left. But that would not necessarily harm a luxury brand like Bulgari, because customers for its jewelry were probably on the right, said Guenole, the political scientist.

"People who are really rich and vote left are extremely rare." (Editing by Mark John and Peter Graff)